Use of a zwitterionic surfactant together with an anionic ether-containing surfactant as a drag-reducing agent

ABSTRACT

The present invention relates to the use of a zwitterionic surfactant in combination with an ether sulphate or ether carboxylate surfactant in a water-based system as a drag-reducing agent. The combination has besides a high drag-reducing effect also a low sensitivity to hard water.

The present invention relates to the use of a zwitterionic surfactanttogether with an ether sulphate or ether carboxylate surfactant in awater-based system as a drag-reducing agent.

Surfactants with the ability to form extremely long, cylindricalmicelles have, in recent years, attracted a great interest asdrag-reducing additives to systems with circulating water, especiallythose destined for heat or cold distribution.

An important reason for this interest is that, although one desires tomaintain a laminar flow in the conduits, one wishes at the same time tohave turbulence in the heat exchangers to achieve therein a high heattransfer per unit area.

As may easily be understood, fibres or chain polymers are unable toprovide this double function which, however, can be achieved withthread-like micelles, since the micelles, which are responsible for thedrag reduction, can be destructed by mechanical devices either withinthe heat exchangers or immediately before them. Thus a turbulent flowwill be created within said heat exchangers. In the tube after theexchanger the micelles will form again rather rapidly and the dragreduction will thus be restored.

The thread-like micelles are distinguished by operating in a fairlydisorderly fashion at low Reynold's numbers (below 10⁴), having no oronly a very slight effect on the flow resistance. At higher Reynold'snumbers (above 10⁴), the micelles are paralleled and result in a dragreduction very close to that which is theoretically possible. At evenhigher Reynold's numbers (e.g. above 10⁵) the shear forces in the liquidbecome so high that the micelles start to get torn and the drag-reducingeffect rapidly decreases as the Reynold's number increases above thisvalue.

The range of Reynold's numbers within which the surface-active agentshave a significant drag-reducing effect is dependent on theconcentration, the range increasing with the concentration.

By choosing the right concentration of surface-active agents andsuitable flow rates in conduits and adequate devices before or in theheat exchangers, it is thus possible to establish a laminar flow in theconduits and turbulence in the heat exchangers. Thus, the dimensions ofthe conduits can be kept at a low level and the pump size, or the numberof pump stations, and consequently the pump work, can alternatively bereduced while retaining the same tubular dimensions.

In WO 96/28527 a drag reducing agent is disclosed, which comprises abetaine surfactant in combination with a sulphonate or sulphatesurfactant. This drag-reducing agent is effective within comparativelylarge temperature ranges. However, the sulphate surfactant is rathersensitive to hard water, while the sulphonate surfactant is not regardedas easily biodegradable under anaerobic conditions.

It has now surprisingly been found that essential improvements areachieved by the use of a zwitterionic surfactant having the formula

R is a group containing saturated or unsaturated aliphatic or acyl groupwith 10-24 carbon atoms, R₆ and R₇ are independently of each other analkyl group of 1-4 carbon atoms or an hydroxyalkyl group of 2-4 carbonatoms, and R₄ is an alkylene group of 1-4 carbon atoms, preferably CH₂or a group

where R₅ is an alkyl group of 1-3 carbon atoms, in combination with ananionic ether surfactant having the general structure

R₁(OA)_(n)B, R₁O(AO)_(n)C_(m)H_(2m)D or R₃NH(AO)_(n)C_(m)H_(2m)D or amixture thereof, where R₁ is a hydrocarbon group of 10-24 carbon atoms,R₃ is an acyl group of 10-24 carbon atoms, A is an alkylene group having2-4 carbon atoms, n is a number from 1 to 10, m is 1-4, B is a sulphategroup OSO₃M, D is a carboxylate group COOM, and M is a cationic,preferably monovalent group, in a weight proportion between thezwitterionic surfactant and the anionic ether surfactant or ethersurfactants of from 100:1 to 1:1, preferably from 50:1 to 2:1, as adrag-reducing agent in a flowing water-based liquid system. By“water-based” is meant that at least 50% by weight, preferably at least90% by weight, of the water-based liquid system consists of water. Thetotal amount of the zwitterionic surfactant and the anionic ethersurfactants may vary within wide limits depending on the conditions butis generally 0.1-10 kg/m³ of the water-based system. The combinations ofthe zwitterionic and the anionic ether surfactants are especially suitedfor use in water-based systems flowing in long conduits, fordistribution of heat or cold.

The group R in the zwitterionic surfactant is suitably an aliphaticgroup or a group R′NHC₃H₆, where R′ designates an acyl group with 10-24carbon atoms. Preferably the zwitterionic surfactant has the generalformula

where R is the aliphatic group or the group R′NHC₃H₆— where R′ has themeaning mentioned above. In the anionic ether surfactant the hydrophobicgroup R₁ can be aliphatic or aromatic, straight or branched, saturatedor unsaturated. Furthermore, the groups A are preferably ethylene, n ispreferably a number from 1-5 and C_(m)H_(2m) is preferably methylene orthe group

where R₈ is an alkyl group of 1-3 carbon atoms. The group M ispreferably sodium and potassium.

Both the zwitterionic surfactant and the anionic ether surfactants arereadily biodegradable and tolerant towards hard water and electrolytesand said combination gives an excellent drag reducing effect within awide temperature range. Thus, the drag-reducing additives may be used ina cooling media at temperatures below 20° C., when using surfactants,where the groups R and R′ have 12-16 carbon atoms, and in aheat-transfer medium at a temperature in the range of 50-120° C., whenusing surfactants where the groups R, and R′ contain 18, 20 or 22 carbonatoms or more. The number of carbon atoms in the hydrophobic groups R,R′, R₁ and R₃ will affect the useful temperature range for the mixtureso that a high number will give products suitable for high temperaturesand vice versa. The groups R and R₁ can suitably be dodecyl, tetradecyl,hexadecyl, octadecyl, oleyl, eicosyl, docosyl, rape seed alkyl andtallow alkyl and the groups R′ and R₃ the corresponding acyl groups.Also aromatic groups, such as nonylphenol, may be used.

Furthermore, the zwitterionic and anionic surfactants are suitablychosen in such a manner that the crystallisation temperature for thecombination is suitably below the lowest temperature for which thewater-based system is intended. Suitably the zwitterionic surfactant iscombined with an anionic ether sulphate surfactant where n is 1-5 and OAoxyethylene, since the ether sulphate is easy to produce and gives incombination with the zwitterionic surfactant excellent drag-reducingeffects.

The zwitterionic surfactant can be produced by reacting a compound ofthe formula RNR₆R₇, where R has the meaning mentioned above, withNa-chloroacetate at 70-80° C. and a constant pH-value of 9.5 in a mediumof a lower alcohol and water. To obtain a good drag reducing effect itis essential that the amount of the amine reactant in the zwitterionicproduct used is low. If a low chloride content in the product isnecessary the reaction can preferably be made in isopropanol with thelowest water content possible, whereby the sodium chloride formed in thereaction will crystallise out of the product and may be removed byfiltration or centrifugation. Another route to a chloride-free productis to quaternize the amine reactant with ethylene oxide in the presenceof an acid catalyst and then dehydrogenate the resulting product to thedesired zwitterionic surfactant.

The anionic ether surfactants suitable for use in accordance with theinvention are well-known products and so are also the productionmethods. Typical examples are aliphatic mono(oxyethylene) sulphates,alkyl di(oxyethylene) sulphates and alkyl tri(oxyethylene) sulphatesderived from ethoxylated alcohols by sulphation with SO₃ and thecorresponding carboxylates obtained by reacting said ethoxylated alcoholand a halogenated carboxylate having the formula HalC_(m)H_(2m)COOM,where Hal is chloride or bromide and M and m have the meanings mentionedabove. The amido ether carboxylate may be produced according towell-known methods including the reaction of said halogenatedcarboxylate and the amidoalkoxylate R₃NH(AO)_(n)H, where R₃, A and nhave the meanings mentioned above.

The choice of the zwitterionic surfactant and the anionic ethersurfactant will depend of the temperature of the water-based system. Atlow temperature the number of carbon atoms will normally be lower thanat high temperature while the number of oxyalkylene will normally behigher at lower temperatures than at higher temperatures.

A convenient way to determine the right proportion between thezwitterionic surfactant and the anionic surfactant for a certain type ofwater is to make up a solution of e.g. 0.500 kg/m³ of the zwitterionicsurfactant in the appropriate water in a 50 ml glass beaker with amagnetic stirrer and keep the temperature in the middle of the intendedtemperature range for the system. This solution is then titrated with asolution of the anionic ether surfactant with a concentration of 10kg/m³ in the appropriate water until the originally formed vortex hasdisappeared.

Apart from the zwitterionic and anionic surfactant, the water-basedsystem may contain a number of conventional components such as corrosioninhibitors, anti-freeze and bactericides.

The present invention will now be further illustrated with the aid ofthe following examples.

EXAMPLE 1

The drag reducing temperature interval was determined in the beaker testdescribed above. In the beaker test the surfactant mixture was stirredat a constant rotation speed of 700 r/min using a combined magneticstirrer and heating plate. The absence of vortex or a vortex of max. 2mm was equal to drag reducing conditions. In temperatures above 100° C.a glass pressure reactor was used.

From stock solutions mixtures of betaine and anionic surfactant wereprepared. The mixtures were diluted with water, with hardness accordingto the tables below, to 1000 ppm betaine and a total volume of 40 ml ina 50 ml beaker. The amount of anionic surfactant is given as ppm inbrackets. The pH was adjusted to 9-10 with ammonia.

TABLE 1 N-behenyl betaine (1000 ppm) for heating systems DR interval(700 r/min) Anionic surfactant 0° dH 3° dH 8° dH Sodium dodecyl sulphate55-120 (30) 55-68 (30) 55-68 (30) Sodium dodecyl-(EO)₃-sulphate 55-123(40)  55-108 (40) 50-78 (40) Dodecyl amide-(EO)₂-carboxylate 55-104 (40)48-95 (40) 49-86 (40) Nonylphenol-(EO)₃-carboxylate 53-97 (40)  49-94(40) 49-74 (40)

A drag reducing agent containing an anionic ether surfactant exhibit anessentially better drag reducing effect in water of 3° dH and 8° dH thanthe agent containing alkyl sulphate.

EXAMPLE 2

The present example is performed according to the previously describedscreening test.

In order to determine the right amount of anionic surfactant the betainesolution was kept at 13° C. in the test beaker with the magnetic stirrerrunning at 700 r.p.m and titrated with a water solution of the anionicsurfactant until the vortex disappeared. The resulting concentration ofanionic surfactant is given as ppm in brackets after the temperaturerange within which the composition has been found to give a dragreducing effect. The clear point (CP) of the solution is given in ° C.

The concentration of the N-myristyl-betaine, the zwitterionic surfactantused in this example, was 1000 ppm in all tests.

TABLE 2 N-myristyl-betaine (1000 ppm) in mixture with anionic surfactantfor cooling systems DR interval (700 r/min) Anionic surfactant 0° dH 3°dH 8° dH Dodecyl benzene sulphonate No effect 0-29 3-25 (0-1130) (430)(980) CP 0° C.  CP 0° C. CP 35° C. Sodium dodecyl-(EO)₃-sulphate 0-43(288) 0-27 (550) 2-25 (510) CP 0° C.  CP 0° C.  CP 2° C. Sodium dodecylsulphate 6-43 (400) 0-39 (336) 4-43 (360) CP 6° C. CP 14° C. CP 20° C.

These formulations are intended for comfort cooling circuits where thetemperature range normally is between 4 and 15° C.

As can be seen, the dodecyl glycolether sulphate is working well in thistemperature range whereas the dodecyl benzene sulphonate formulationgives no drag reduction in deionized water and sodium dodecyl sulphatedoes not work satisfactory in water of 8° dH at low temperatures.

Furthermore the use of sodium dodecyl sulphate is hampered in practicalapplications by the precipitation both of the sodium and the calciumsalts.

1-10. (canceled)
 11. A method for reducing drag in a flowing water-basedliquid system flowing in conduits for the efficient distribution of heator cold, which method comprises adding to the water-based liquid systema combination of: i.) a zwitterionic surfactant having the formula

wherein R is a group containing a saturated or unsaturated aliphatic oracyl group with 10-24 carbon atoms, or a group R′NHC₃H₆— where R′ is anacyl group having 10-24 carbon atoms, R₆ and R₇ are independently ofeach other an alkyl group of 1-4 carbon atoms or an hydroxyalkyl groupof 2-4 carbon atoms, and R₄ is an alkylene group of 1-4 carbon atoms;and ii.) an anionic ether surfactant having the general structure R₁(OA)_(n)B, R₁O(AO)_(n)C_(m)H_(2m)D or R₃NH(AO)_(n)C_(m)H_(2m)D or amixture thereof, where R₁ is a hydrocarbon group of 10-24 carbon atoms,R₃ is an acyl group of 10-24 carbon atoms, A is an alkylene group having2-4 carbon atoms, n is a number from 1 to 10, m is 1-4, B is a sulphategroup OSO₃M and D is a carboxylate group COOM, in which M is a cationicgroup; wherein the weight proportion between the zwitterionic surfactantand the anionic ether surfactant is from 100:1 to 1:1.
 12. A methodaccording to claim 11, wherein the zwitterionic surfactant has thegeneral formula

and wherein R is the aliphatic group or the group R′NHC₃H₆— where R′ isthe acyl group.
 13. A method according to claim 11 wherein thecrystallization temperature for the combination of the zwitterionicsurfactant and the anionic ether is below the lowest temperature forwhich the water-based system is intended.
 14. A method according toclaim 11 wherein the zwitterionic surfactant and anionic ethersurfactant is added in a total amount of about 0.1 to about 10 kg/m³ ofthe water-based system.
 15. A method according to claim 11 wherein thewater-based system is a cooling medium with a temperature of about 20°C. or lower.
 16. A method according to claim 12 wherein the groups R andR′ contain 18-24 carbon atoms.
 17. A method according to claim 16wherein the group R and R₁ contain 12-16 carbon atoms.
 18. A methodaccording to claim 11 wherein the groups R₄ and C_(m)H_(2m) designatemethylene.
 19. A method according to claim 11 wherein the anionic ethersurfactant is an ether sulphate, where n is 1-5 and OA is oxyethylene.20. A drag reducing agent for a flowing water-based liquid system, saiddrag reducing agent comprising a combination of i.) a zwitterionicsurfactant having the formula

wherein R is a group containing a saturated or unsaturated aliphatic oracyl group with 10-24 carbon atoms, or a group R′NHC₃H₆— where R′ is anacyl group having 10-24 carbon atoms, R₆ and R₇ are independently ofeach other an alkyl group of 1-4 carbon atoms or an hydroxyalkyl groupof 2-4 carbon atoms, and R₄ is an alkylene group of 1-4 carbon atoms;and ii.) an anionic ether surfactant having the general structureR₁(OA)_(n)B, R₁O(AO)_(n)C_(m)H_(2m)D or R₃NH(AO)_(n)C_(m)H_(2m)D or amixture thereof, where R₁ is a hydrocarbon group of 10-24 carbon atoms,R₃ is an acyl group of 10-24 carbon atoms, A is an alkylene group having2-4 carbon atoms, n is a number from 1 to 10, m is 1-4, B is a sulphategroup OSO₃M and D is a carboxylate group COOM, in which M is a cationicgroup; wherein the weight proportion between the zwitterionic surfactantand the anionic ether surfactant is from 100:1 to 1:1.
 21. A flowingwater based liquid system comprising the drag reducing agent of claim20.